During hydrotreating of hydrocarbon feedstocks, catalyst activity decreases with time on stream as coke accumulates on the catalyst surface. Eventually, the catalyst must be regenerated by burning off the coke in air to restore activity. Unfortunately, in most cases, the regenerated hydrotreating catalyst has a lower activity than the original fresh catalyst and must subsequently be used in less demanding, lower valued service.
Increasingly stringent environmental regulations will require significant reductions in the sulfur content of transportation fuels. For example, by the end of this decade, maximum sulfur levels for distillate fuel will be limited to 10 wppm in Europe and Japan and 15 wppm in North America. Meeting these ultra-low sulfur requirements, without undercutting distillate endpoint or expensive modifications to existing refineries, may require catalysts with increasingly higher activities. Such higher activity hydrotreating catalysts are typically higher cost due to higher metal loadings. Due to these higher costs, it would be desirable to regenerate and reuse these spent catalysts. However, as noted above, regeneration procedures often result in catalysts with reduced activities.
What is needed is a method for rejuvenating high activity hydroprocessing catalysts that allows reuse of the rejuvenated catalyst without having to settle for use in a lower value, less demanding service.